T cell adoptive immunotherapy is a promising approach for cancer treatment. This strategy utilizes isolated human T cells that have been genetically-modified to enhance their specificity for a specific tumor associated antigen. Genetic modification may involve the expression of a chimeric antigen receptor or an exogenous T cell receptor to graft antigen specificity onto the T cell. By contrast to exogenous T cell receptors, chimeric antigen receptors derive their specificity from the variable domains of a monoclonal antibody. Thus, T cells expressing chimeric antigen receptors (CAR T cells) induce tumor immunoreactivity in a major histocompatibility complex non-restricted manner. To date, T cell adoptive immunotherapy has been utilized as a clinical therapy for a number of cancers, including B cell malignancies (e.g., acute lymphoblastic leukemia (ALL), B cell non-Hodgkin lymphoma (NHL), and chronic lymphocytic leukemia), multiple myeloma, neuroblastoma, glioblastoma, advanced gliomas, ovarian cancer, mesothelioma, melanoma, and pancreatic cancer.
Despite its potential usefulness as a cancer treatment, adoptive immunotherapy with CAR T cells has been limited, in part, by expression of the endogenous T cell receptor on the cell surface. CAR T cells expressing an endogenous T cell receptor may recognize major and minor histocompatibility antigens following administration to an allogeneic patient, which can lead to the development of graft-versus-host-disease (GVHD). As a result, clinical trials have largely focused on the use of autologous CAR T cells, wherein a patient's T cells are isolated, genetically-modified to incorporate a chimeric antigen receptor, and then re-infused into the same patient. An autologous approach provides immune tolerance to the administered CAR T cells; however, this approach is constrained by both the time and expense necessary to produce patient-specific CAR T cells after a patient's cancer has been diagnosed.
Thus, it would be advantageous to develop “off the shelf” CAR T cells, prepared using T cells from a third party donor, that have reduced expression of the endogenous T cell receptor and do not initiate GVHD upon administration. Such products could be generated and validated in advance of diagnosis, and could be made available to patients as soon as necessary. Therefore, a need exists for the development of allogeneic CAR T cells that lack an endogenous T cell receptor in order to prevent the occurrence of GVHD.
Genetic modification of genomic DNA can be performed using site-specific, rare-cutting endonucleases that are engineered to recognize DNA sequences in the locus of interest. Methods for producing engineered, site-specific endonucleases are known in the art. For example, zinc-finger nucleases (ZFNs) can be engineered to recognize and cut pre-determined sites in a genome. ZFNs are chimeric proteins comprising a zinc finger DNA-binding domain fused to the nuclease domain of the FokI restriction enzyme. The zinc finger domain can be redesigned through rational or experimental means to produce a protein that binds to a pre-determined DNA sequence ˜18 basepairs in length. By fusing this engineered protein domain to the FokI nuclease, it is possible to target DNA breaks with genome-level specificity. ZFNs have been used extensively to target gene addition, removal, and substitution in a wide range of eukaryotic organisms (reviewed in Dural et al. (2005), Nucleic Acids Res 33, 5978). Likewise, TAL-effector nucleases (TALENs) can be generated to cleave specific sites in genomic DNA. Like a ZFN, a TALEN comprises an engineered, site-specific DNA-binding domain fused to the FokI nuclease domain (reviewed in Mak et al. (2013), Curr Opin Struct Biol. 23:93-9). In this case, however, the DNA binding domain comprises a tandem array of TAL-effector domains, each of which specifically recognizes a single DNA basepair. A limitation that ZFNs and TALENs have for the practice of the current invention is that they are heterodimeric, so that the production of a single functional nuclease in a cell requires co-expression of two protein monomers.
Compact TALENs have an alternative endonuclease architecture that avoids the need for dimerization (Beurdeley et al. (2013), Nat Commun. 4:1762). A Compact TALEN comprises an engineered, site-specific TAL-effector DNA-binding domain fused to the nuclease domain from the I-TevI homing endonuclease. Unlike FokI, I-TevI does not need to dimerize to produce a double-strand DNA break so a Compact TALEN is functional as a monomer.
Engineered endonucleases based on the CRISPR/Cas9 system are also know in the art (Ran et al. (2013), Nat Protoc. 8:2281-2308; Mali et al. (2013), Nat Methods 10:957-63). A CRISPR endonuclease comprises two components: (1) a caspase effector nuclease, typically microbial Cas9; and (2) a short “guide RNA” comprising a ˜20 nucleotide targeting sequence that directs the nuclease to a location of interest in the genome. By expressing multiple guide RNAs in the same cell, each having a different targeting sequence, it is possible to target DNA breaks simultaneously to multiple sites in the genome. Thus, CRISPR/Cas9 nucleases are suitable for the present invention. The primary drawback of the CRISPR/Cas9 system is its reported high frequency of off-target DNA breaks, which could limit the utility of the system for treating human patients (Fu et al. (2013), Nat Biotechnol. 31:822-6).
Homing endonucleases are a group of naturally-occurring nucleases that recognize 15-40 base-pair cleavage sites commonly found in the genomes of plants and fungi. They are frequently associated with parasitic DNA elements, such as group 1 self-splicing introns and inteins. They naturally promote homologous recombination or gene insertion at specific locations in the host genome by producing a double-stranded break in the chromosome, which recruits the cellular DNA-repair machinery (Stoddard (2006), Q. Rev. Biophys. 38: 49-95). Homing endonucleases are commonly grouped into four families: the LAGLIDADG (SEQ ID NO:7) family, the GIY-YIG family, the His-Cys box family and the HNH family. These families are characterized by structural motifs, which affect catalytic activity and recognition sequence. For instance, members of the LAGLIDADG (SEQ ID NO:7) family are characterized by having either one or two copies of the conserved LAGLIDADG (SEQ ID NO:7) motif (see Chevalier et al. (2001), Nucleic Acids Res. 29(18): 3757-3774). The LAGLIDADG (SEQ ID NO:7) homing endonucleases with a single copy of the LAGLIDADG (SEQ ID NO:7) motif form homodimers, whereas members with two copies of the LAGLIDADG (SEQ ID NO:7) motif are found as monomers.
I-CreI (SEQ ID NO: 6) is a member of the LAGLIDADG (SEQ ID NO:7) family of homing endonucleases that recognizes and cuts a 22 basepair recognition sequence in the chloroplast chromosome of the algae Chlamydomonas reinhardtii. Genetic selection techniques have been used to modify the wild-type I-CreI cleavage site preference (Sussman et al. (2004), J. Mol. Biol. 342: 31-41; Chames et al. (2005), Nucleic Acids Res. 33: e178; Seligman et al. (2002), Nucleic Acids Res. 30: 3870-9, Arnould et al. (2006), J. Mol. Biol. 355: 443-58). More recently, a method of rationally-designing mono-LAGLIDADG (SEQ ID NO:7) homing endonucleases was described that is capable of comprehensively redesigning I-CreI and other homing endonucleases to target widely-divergent DNA sites, including sites in mammalian, yeast, plant, bacterial, and viral genomes (WO 2007/047859).
As first described in WO 2009/059195, I-CreI and its engineered derivatives are normally dimeric but can be fused into a single polypeptide using a short peptide linker that joins the C-terminus of a first subunit to the N-terminus of a second subunit (Li et al. (2009), Nucleic Acids Res. 37:1650-62; Grizot et al. (2009), Nucleic Acids Res. 37:5405-19). Thus, a functional “single-chain” meganuclease can be expressed from a single transcript.
The use of engineered meganucleases for cleaving DNA targets in the human T cell receptor alpha constant region was previously disclosed in International Publication WO 2014/191527. The '527 publication discloses variants of the I-OnuI meganuclease that are engineered to target a recognition sequence (SEQ ID NO:3 of the '527 publication) within exon 1 of the TCR alpha constant region gene. Although the '527 publication discusses that a chimeric antigen receptor can be expressed in TCR knockout cells, the authors do not disclose the insertion of the chimeric antigen receptor coding sequence into the meganuclease cleavage site in the TCR alpha constant region gene.
The use of other nucleases and mechanisms for disrupting expression of the endogenous TCR have also been disclosed. For example, the use of zinc finger nucleases for disrupting TCR genes in human T cells was described by U.S. Pat. No. 8,956,828 and by U.S. Patent Application Publication No. US2014/0349402. U.S. Publication No. US2014/0301990 describes the use of zinc finger nucleases and transcription-activator like effector nucleases (TALENs), and a CRISPR/Cas system with an engineered single guide RNA for targeting TCR genes in an isolated T cell. U.S. Patent Application Publication No. US2012/0321667 discloses the use of small-hairpin RNAs that target nucleic acids encoding specific TCRs and/or CD3 chains in T cells.
However, the present invention improves upon the teachings of the prior art. The present inventors are the first to teach genetically-modified cells that comprise an exogenous polynucleotide sequence (e.g., a chimeric antigen receptor or exogenous TCR coding sequence) inserted into the human TCR alpha constant region gene, which simultaneously disrupts expression of the endogenous T cell receptor at the cell surface. Further, the prior art does not teach the meganucleases or the recognition sequences described herein, or their use for producing such genetically-modified cells.